Articulated wind turbine blades

ABSTRACT

A blade assembly for a wind turbine has a hub, a plurality of inboard and outboard blades, and a plurality of cables. The inboard blades are spaced apart from one another and are mounted on the hub. Each outboard blade is pivotally connected to one of the inboard blades such that it is capable of rotation to a desired swept angle relative to the inboard blade to which it is connected. The cables extend between the outboard blades and the inboard blades to actuate rotation of the outboard blades to the desired swept angle.

BACKGROUND

The invention relates to wind turbines, and in particular, to windturbines with articulated blades.

With the diminishing global supply of fossil fuel, renewable sources ofenergy such as power generated from wind turbines is gaining anincreasing share of the electric power market. Thus, generatingelectrical power more efficiently with wind turbines has becomeincreasingly important to lowering the overall cost of electricity.

It is known that the conversion efficiency of wind generated kineticenergy to electric power is proportional to the square of the length ofthe blades of a wind turbine. Thus, increasing the length of the bladesallows the wind turbine to produce power more efficiently. Lengthyblades currently face three major challenges that have negativelyimpacted their implementation on wind turbines. First, lengthy blades(current blades can have a length of up to about 50 meters, future bladelengths of up to 80 meters have been contemplated) can be difficult totransport and install. Special large trucks are needed to transport theblades from the manufacturing site along routes to an on-shoreimplementation site. The routes must be carefully planned so as toaccommodate the large trucks and cargo. Specially designed tall cranesmay also be required to hoist the blades to the wind turbine tower forinstallation. In view of these and other challenges,transportation/installation cost can be as high as one third of themanufacturing cost of the blades.

Lengthy blades also have high velocity gradients from the root of theblade to the tip of the blade. High velocity gradients complicate theengineering and fabrication of the wind turbine and blades. Forinstance, blades (especially those with high velocity gradients) must bedesigned with a degree of twist (commonly called pitch) from root to tipso as to optimize performance of the blade for a most common windvelocity expected to be experienced at the installation site. Addingtwist to blades adds to the complexity of their manufacturing and theircost. Once installed, the twist of the blade commonly remains fixed suchthat if the wind blows with an unpredicted (non-optimized) speed theconversion efficiency of the wind turbine is reduced.

Additionally, wind turbines utilizing lengthy blades must be shut downduring periods of high wind so as to avoid damaging wind turbine partssuch as the blades, bearings, gears and support tower. In contrast, windturbines that utilize shorter blades can operate in higher windconditions without having to be shut down.

Lengthy blades commonly have a low bending stiffness which cannegatively impact the wind turbine conversion efficiency and windturbine operating life through blade deformation and changes to thenatural frequency of the blade. Measures such as extra materialreinforcement may be required to reduce blade deformation and changes inthe natural frequency of the blade. However, these measures increase themanufacturing cost and weight of the blade.

SUMMARY

A blade assembly for a wind turbine has a hub, a plurality of inboardand outboard blades, and a plurality of cables. The inboard blades arespaced apart from one another and are mounted on the hub. Each outboardblade is pivotally connected to one of the inboard blades such that itis capable of rotation to a desired swept angle relative to the inboardblade to which it is connected. The cables extend between the outboardblades and the inboard blades to actuate rotation of the outboard bladesto the desired swept angle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a first embodiment of a wind turbinehaving articulated inboard blades and outboard blades with the outboardblades disposed in a first fully extended position.

FIG. 1B is a schematic view of the wind turbine from FIG. 1A with theoutboard blades pivoted to a second position.

FIG. 2 is a sectional view through one of the outboard blades of thewind turbine from FIGS. 1A and 1B illustrating the connection betweenthe outboard blade and a first cable.

FIG. 3A is a schematic view of another embodiment of the wind turbinehaving articulated inboard blades and outboard blades with the outboardblades disposed in a first fully extended position.

FIG. 3B a schematic view of the wind turbine from FIG. 3A with theoutboard blades pivoted to a second position.

FIG. 4 is a sectional view through one of the outboard blades of thewind turbine from FIGS. 3A and 3B illustrating the connection betweenthe outboard blade and a first cable and a second cable.

DETAILED DESCRIPTION

As illustrated in FIGS. 1A and 1B, the present invention describes awind turbine 10A with a plurality of articulated blades comprisinginboard blades 12A, 12B, and 12C and outboard blades 14A, 14B, and 14C.Wind turbine 10A includes a hub 16, a winch 18, a drive device 20, andcables 22A, 22B, and 22C. Inboard blades 12A, 12B, and 12C includepulleys 24A, 24B, and 24C. Outboard blades 14A, 14B, and 14C includeselbows 26A, 26B, and 26C, and each outboard blade 14A, 14B, and 14C isbiased into a first fully extended position illustrated in FIG. 1A byspring loaded hinges 28A, 28B, and 28C.

Outboard blades 14A, 14B, and 14C are pivotally connected to inboardblades 12A, 12B, and 12C. Thus, each outboard blade 14A, 14B, and 14Ccan be rotated to a swept angle Ψ_(a), Ψ_(b), and Ψ_(c) relative toinboard blade 12A, 12B, and 12C to which it is connected. Inboard blades12A, 12B, and 12C spaced apart (in the embodiment shown at 120°intervals from one another) and are fixidly mounted on hub 16 of windturbine 10A. Inboard blades 12A, 12B, and 12C extend outward from hub 16to the pivot connections with outboard blades 14A, 14B, and 14C. Asillustrated in FIGS. 1A and 1B, outboard blades 14A, 14B, and 14C pivotaround axes that can be aligned with but are spaced apart from an axis Arotation of hub 16.

Hub 16 houses components such as the generator(s) and drive device 20(illustrated in phantom) such as the gearbox for wind turbine 10A. Drivedevice 20 can also be a device such as an electric motor that is solelydedicated to rotating outboard blades 14A, 14B, and 14C to desired sweptangle Ψ_(a), Ψ_(b), and Ψ_(c) that conditions dictate. Drive device 20is connected to rotate winch 18 (or similar device) that is alsodisposed in hub 16.

Cables 22A, 22B, and 22C can comprise high strength nylon or steel cableor wire rope or similar linkage. Cables 22A, 22B, and 22C wrap aroundwinch 18 and extend therefrom to pulleys 24A, 24B, and 24C mountedwithin or on a structural portion of inboard blades 12A, 12B, and 12C.Thus, cables 22A, 22B, and 22C can extend from hub 16 either underneathor outside of the skin of inboard blades 12A, 12B, and 12C. From pulleys24A, 24B, and 24C cables 22A, 22B, and 22C extend to connect to elbows26A, 26B, and 26C of the preceding (as defined by direction of rotationof hub 16) outboard blades 14A, 14B, and 14C. For example, with windturbine 10A undergoing counterclockwise rotation as shown in FIGS. 1Aand 1B, cable 22B connects to elbow 26A of the preceding outboard blade14A and extends to pulley 24B mounted on/in receding inboard blade 12B.From pulley 24B, cable 22B extends along inboard blade 12B into hub 16to wrap around winch 18.

In the embodiment shown in FIGS. 1A and 1B, the pivot connectionsbetween outboard blades 14A, 14B, and 14C and inboard blades 12A, 12B,and 12C have spring loaded hinges 28A, 28B, and 28C disposed adjacentthereto. Spring loaded hinges 28A, 28B, and 28C are capable of biasingoutboard blades 14A, 14B, and 14C into the fully extended position withmaximum blade sweep illustrated in FIG. 1A.

The pivotal arrangement of the blades of wind turbine 10A allows eachoutboard blade 14A, 14B, and 14C to vary its swept angle Ψ_(a), Ψ_(b),and Ψ_(c) relative to outboard blade 14A, 14B, and 14C to which it isconnected. By varying swept angles Ψ_(a), Ψ_(b), and Ψ_(a), wind turbine10A can vary the sweep of blades 12A-12C and 14A-14C without changingthe overall length of blades 12A-12C and 14A-14C. By varying swept angleΨ_(a), Ψ_(b), and Ψ_(c) as desired, conversion efficiency for windturbine 10A can be optimized in view of wind conditions, drag, and otherforces at the installation site.

To vary swept angles Ψ_(a), Ψ_(b), and Ψ_(a), outboard blades 14A, 14B,and 14C are actuated to pivot relative to inboard blades 12A, 12B, and12C by cables 22A, 22B, and 22C. Cables 22A, 22B, and 22C are tightenedor loosened to a desired tension by winding/unwinding rotation of winch18 which is driven by drive device 20. The tension force (or lackthereof) of cables 22A, 22B, and 22C along with inertia and drag forcescounter the bias force of hinges 28A, 28B, and 28C to move each outboardblade 14A, 14B, and 14C to desired swept angles Ψ_(a), Ψ_(b), and Ψ_(a).For example, if tension on cables 22A, 22B, and 22C is reduced orreleased, this allows the bias force of hinges 28A, 28B, and 28C toreturn outboard blades 14A, 14B, and 14C into the fully extendedposition with maximum blade sweep illustrated in FIG. 1A. If tension oncables 22A, 22B, and 22C is increased above the bias force exerted byhinges 28A, 28B, and 28C, outboard blades 14A, 14B, and 14C will rotateto a position such as the one shown in FIG. 1B.

In instances of low wind conditions such as those illustrated in FIG.1A, outboard blades 14A, 14B, and 14C could be fully extended to thefully extend position with maximum blade sweep to achieve maximumconversion efficiency. In the fully extended position, each swept angleΨ_(a), Ψ_(b), and Ψ_(c) extends substantially 180° between correspondinginboard blades 12A, 12B, and 12C and outboard blades 14A, 14B, and 14C.In instances of high wind conditions such as those illustrated in FIG.1B, outboard blades 14A, 14B, and 14C are pivoted to desired swept angleΨ_(a), Ψ_(b), and Ψ_(c) that is less than 180° with respect tocorresponding connected inboard blades 12A, 12B, and 12C. Such anarrangement could keep wind turbine 10A from having to shut down inhigher wind conditions by reducing drag and other forces on wind turbine10A.

Wind turbine 10A would also benefit from reduced transportation andinstallation costs as each blade assembly comprising inboard blades 12A,12B, and 12C and outboard blades 14A, 14B, and 14C could be shipped andinstalled with reduced need for special trucks, routes, and cranes aseach blade individually would have a reduced length (until assembled)when compared with similar conventional wind turbine blade designshaving a similar operational blade sweep.

Additionally, cables 22A, 22B, and 22C would act to stabilize andstiffen inboard blades 12A, 12B, and 12C and outboard blades 14A, 14B,and 14C without adding a great deal of additional weight to thosestructures. Thus, wind turbine 10A would benefit from improved bendingstiffness thereby reducing the likelihood of blade deformation andchanges to the natural frequency of blades 12A-12C and 14A-14C.

FIG. 2 shows a sectional view of elbow 26B of outboard blade 14B fromFIG. 1A. Cable 22C terminates at elbow 26B using conventional means suchas a loop 30 to connect it to outboard blade 14B. Other conventionalmeans and methods of cable/wire termination/connection can includeswagging, clamping, clipping, splicing, hooks, eyes, threaded rods,studs, forks or the equivalent. Loop 30 attaches cable 22C to hook 32. Ahook 32, or suitable alternative, is attached to a structural memberwithin outboard blade 14B.

FIGS. 3A and 3B show another embodiment of wind turbine 10B. In mostrespects wind turbine 10B operates in the same manner as and hasidentical components to wind turbine 10A. However, wind turbine 10Bincludes extender cables 22AA, 22BB, and 22CC in addition to cables 22A,22B, and 22C, and pulleys 24AA, 24BB, and 24CC in addition to pulleys24A, 24B, and 24C.

Similar to wind turbine 10A, wind turbine 10B has outboard blades 14A,14B, and 14C that are pivotally connected to inboard blades 12A, 12B,and 12C. Inboard blades 12A, 12B, and 12C are spaced apart (in theembodiment shown at 120° intervals from one another) and are fixidlymounted on hub 16 of wind turbine 10B. Inboard blades 12A, 12B, and 12Cextend outward from hub 16 to the pivot connections with outboard blades14A, 14B, and 14C. Each outboard blade 14A, 14B, and 14C can be rotatedto swept angle Ψ_(a), Ψ_(b), and Ψ_(c) relative to inboard blade 12A,12B, and 12C to which it is connected.

However, inboard blades 12A, 12B, and 12C have additional pulleys 24AA,24BB, and 24CC mounted within or on a structural portion thereof. Cables22AA, 22BB, and 22CC wrap around winch 18 in the opposite direction ascables 22A, 22B, and 22C. From winch 18 cables 22AA, 22BB, and 22CC runto pulleys 24AA, 24BB, and 24CC. Similar to cables 22A, 22B, and 22C,cables 22AA, 22BB, and 22CC can extend from hub 16 either underneath oroutside of the skin of inboard blades 12A, 12B, and 12C. However, frompulleys 24AA, 24BB, and 24CC cables 22AA, 22BB, and 22CC extend in adirection that differs from cables 22A, 22B, and 22C. This directionallows cables 22AA, 22BB, and 22CC to connect to elbows 26A, 26B, and26C of the receding (as defined by direction of rotation of hub 16)outboard blades 14A, 14B, and 14C. Thus, with wind turbine 10Bundergoing counterclockwise rotation as shown in FIGS. 3A and 3B, cable22B connects to elbow 26A of the preceding outboard blade 14A and runsto pulley 24B mounted on/in receding inboard blade 12B and cable 22BBconnects to elbow 26C of the receding outboard blade 14C and extends topulley 24BB. From pulley 24BB, cable 22BB extends along inboard blade12B into hub 16 to wrap around winch 18 in direction opposite that ofcable 22B.

In the embodiment shown in FIGS. 3A and 3B, outboard blades 14A, 14B,and 14C are pivoted relative to inboard blades 12A, 12B, and 12C bycables 22A, 22B, 22C, 22AA, 22BB, and 22CC. Hinges 28A, 28B, and 28Cused with wind turbine 10A are eliminated from wind turbine 10B.

To extend outboard blades 14A, 14B, and 14C into the fully extendedposition with maximum blade sweep illustrated in FIG. 3A, outboardblades 14A, 14B, and 14C are actuated to pivot relative to inboardblades 12A, 12B, and 12C by extender cables 22AA, 22BB, and 22CC. Inparticular, cables 22AA, 22BB, and 22CC are tightened to a desiredtension by winding rotation of winch 18 which is driven by drive device20. This winding rotation acts to extend outboard blades 14A, 14B, and14C by increasing swept angle Ψ_(a), Ψ_(b), and Ψ_(c) up tosubstantially 180°. Indeed, winding rotation of cables 22AA, 22BB, and22CC can increase swept angle Ψ_(a), Ψ_(b), and Ψ_(c) to exceed 180° insome embodiments. The cables 22AA, 22BB, and 22CC act to extend outboardblades 14A, 14B, and 14C (increase swept angle Ψ_(a), Ψ_(b), and Ψ_(a))because the tension force of cables 22AA, 22BB, and 22CC overcomes theforce of cables 22A, 22B, and 22C (and inertia and drag forces) to moveeach outboard blade 14A, 14B, and 14C.

To vary swept angles Ψ_(a), Ψ_(b), and Ψ_(c) from the fully extendedposition shown in FIG. 3A, outboard blades 14A, 14B, and 14C are pivotedby cables 22A, 22B, and 22C. Cables 22A, 22B, and 22C are tensioned bywinding winch 18. This winding also unwinds (decreases tension on)cables 22AA, 22BB, and 22CC. Eventually, the tension force of cables22A, 22B, and 22C along with inertia and drag forces overcome the forceexerted by cables 22AA, 22BB, and 22CC to move each outboard blade 14A,14B, and 14C to desired swept angles Ψ_(a), Ψ_(b), and Ψ_(C).

FIG. 4 shows a sectional view of elbow 26B of outboard blade 14B fromFIG. 3A. Cables 22C and 22AA terminate at elbow 26B with conventionalmeans such as loops 30A and 30B used to connect cables 22C and 22AA tooutboard blade 14B. In other embodiments, cables 22A, 22B, and 22C canterminate at an elbow location that differs from that of the terminationpoints of cables 22AA, 22BB, and 22CC. Other conventional means andmethods of cable/wire termination and connection can include swagging,clamping, clipping, splicing, hooks, eyes, threaded rods, studs, forksor the equivalent. Loops 30A and 30B attach cables 22C and 22AA to hooks32A and 32B, respectively. Hooks 32A and 32B, or suitable alternative,are attached to a structural member on or within outboard blade 14B.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Forexample, while blade assemblies comprising inboard and outboardarticulated blades are specifically described it is recognized that ablade assembly of three or more blades comprising inboard, middle, andoutboard blades, are contemplated in other embodiments. In addition,many modifications may be made to adapt a particular situation ormaterial to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A wind turbine comprising: a hub; a first inboard blade and a second inboard blade, the first inboard blade and second inboard blade spaced apart and mounted on the hub of the wind turbine; a first outboard blade pivotally connected to the first inboard blade and a second outboard blade pivotally connected to the second inboard blade; and a first cable extending between the first outboard blade and the second inboard blade, and connected to a pulley disposed on or within the second inboard blade.
 2. The wind turbine of claim 1, wherein the first cable actuates rotation of the first outboard blade to a desired swept angle relative to the first inboard blade.
 3. The wind turbine of claim 1, further comprising: a third outboard blade pivotally connected to a third inboard blade, the third inboard blade mounted to the hub and spaced apart from the first and second inboard blades; and at least two cables in addition to the first cable, the at least two cables including a second cable extending between the second outboard blade and the third inboard blade and a third cable extending between the third outboard blade and the first inboard blade.
 4. The wind turbine of claim 3, wherein the second cable actuates rotation the second outboard blade to a desired swept angle relative to the second inboard blade and the third cable actuates rotation the third outboard blade to a desired swept angle relative to the third inboard blade.
 5. The wind turbine of claim 1, wherein the first outboard blade and the second outboard blade are each biased toward a first position by spring loaded hinges.
 6. The wind turbine of claim 5, wherein in the first position comprises a fully extended position at which the connected first inboard blade and first outboard blade and the connected second inboard blade and second outboard blade both have a maximum blade sweep, and wherein the first outboard blade has a swept angle of substantially 180° with respect to the first inboard blade, and the second outboard blade has a swept angle of substantially 180° with respect to the second inboard blade.
 7. The wind turbine of claim 1, further comprising at least one extender cable that extends between the second outboard blade and the first inboard blade, and wherein the extender cable can be tightened or loosened to a desired tension by either a dedicated drive device or a gearbox of the wind turbine to rotate the second outboard blade to a desired swept angle relative to the second inboard blade.
 8. The wind turbine of claim 7, wherein the desired swept angle corresponds to a fully extended position at which each connected inboard and outboard blade has a maximum blade sweep, and wherein the second outboard blade has a swept angle of substantially 180° with respect to the second inboard blade.
 9. The wind turbine of claim 1, wherein the first cable connects to a winch inside the hub of the wind turbine, and wherein the first cable can be tightened or loosened to a desired tension by either a dedicated drive device or a gearbox of the wind turbine.
 10. The wind turbine of claim 9, wherein the dedicated drive device comprises an electric motor.
 11. The wind turbine of claim 1, wherein the first cable extends from the pulley underneath the skin of the second inboard blade into the hub of the wind turbine.
 12. A blade assembly for a wind turbine, comprising: a hub; a plurality of inboard blades spaced apart from one another and mounted on the hub of the wind turbine; a plurality of outboard blades, each outboard blade pivotally connected to one of the plurality inboard blades; and a plurality of cables, each cable extending between one of the plurality of outboard blades and one of the plurality of inboard blades, and each cable connecting to a pulley disposed on or within each of the plurality of inboard blades.
 13. The assembly of claim 12, wherein each of the plurality of cables actuates rotation of one of the plurality of outboard blades to a desired swept angle relative to the inboard blade to which it is pivotally connected.
 14. The assembly of claim 13, wherein each of the plurality of cables connects to a winch inside the hub of the wind turbine, and wherein each of the plurality of cables can be tightened or loosened to a desired tension by either a dedicated drive device or a gearbox of the wind turbine to actuate rotation of one of the plurality of outboard blades to the desired swept angle.
 15. The assembly of claim 14, wherein the dedicated drive device comprises an electric motor.
 16. The wind turbine of claim 12, wherein each of the plurality of outboard blades is biased into a first position by spring loaded hinges.
 17. The wind turbine of claim 12, wherein each of the outboard blades is connected to two or more inboard blades by two or more cables, and wherein one of the two or more cables are tightened or loosened to a desired tension by either a dedicated drive device or a gearbox of the wind turbine to rotate each outboard blade to a desired swept angle that corresponds to a fully extended position. 